CN112236811B

CN112236811B - Image processing apparatus and recording medium

Info

Publication number: CN112236811B
Application number: CN201880094312.XA
Authority: CN
Inventors: 伴场裕介
Original assignee: Eizo Corp
Current assignee: Eizo Corp
Priority date: 2018-06-05
Filing date: 2018-06-05
Publication date: 2023-05-09
Anticipated expiration: 2038-06-05
Also published as: CN112236811A; KR20210015904A; US20210233490A1; JPWO2019234825A1; WO2019234825A1; US11276367B2; JP6992176B2; EP3806083A4; KR102453070B1; EP3806083A1

Abstract

In a display in which a single-color pixel and a color pixel are displayed in combination, display at a more appropriate luminance value is realized. An image processing apparatus is provided, which acquires a saturation value of a target pixel or a saturation value of a target small region including the target pixel and peripheral pixels around the target pixel, corrects the target pixel so that a corrected gradation characteristic obtained by correcting the target pixel coincides with a gradation characteristic synthesized by mixing a color gradation characteristic and a monochrome gradation characteristic at a predetermined mixing ratio based on the saturation value, and if the saturation value is c and the mixing ratio of the color gradation characteristic is W, the value of W when c is a variable is represented by W=f (c), and satisfies the following condition: when the saturation value is equal to or greater than a threshold value, there are a saturation value c satisfying f (c) > αg (c) and a multiplier α, and α is equal to or greater than 1.

Description

Image processing apparatus and recording medium

[ field of technology ]

The present invention relates to an image processing apparatus and an image processing program.

[ background Art ]

In recent years, in a medical diagnostic display, a combination of monochrome pixels and color pixels is displayed, whereby comprehensive diagnosis can be performed. When an image is displayed on such a medical diagnostic display, correction using a luminance value of GSDF (Grayscale Standard Display Function) curve defined by DICOM (Digital Imaging and Communications in Medicine) standard is generally performed when monochrome pixels are displayed. In contrast, in the case of displaying color pixels, correction of the luminance value of the γ2.2 curve specified in the sRGB standard is widely used.

Fig. 1 shows the GSDF curves and γ2.2 curves described above. The relationship between the gray value of the input display and the luminance value to be displayed is called "gray characteristic", and as shown in fig. 1, the gray characteristic of a monochrome pixel is different from that of a color pixel. Accordingly, an image processing technique has been developed which appropriately corrects the gradation characteristics of the pixel units of each input image. For example, patent document 1 discloses a technique of combining a color gradation characteristic and a monochrome gradation characteristic by mixing them based on a mixing ratio determined based on a saturation value of a pixel unit or a saturation value of a region unit of an input image.

[ Prior Art literature ]

[ patent literature ]

Japanese patent laid-open publication No. 2016-180787

[ invention ]

[ problem to be solved by the invention ]

However, in the technique of patent document 1, when the saturation value of the pixel unit is used, a diagnostic person who is used to a display that corrects only the color gradation characteristic of the γ2.2 curve for the color image may have a dark color image displayed on the display, and may not be able to make a correct diagnosis. In addition, in the case of using the saturation value of the region unit, there is a possibility that the screen display may collapse according to the saturation calculation result of each region, and an appropriate luminance value may not be output.

The present invention has been made in view of such a situation, and provides an image processing apparatus and an image processing program for realizing display with a more appropriate luminance value in a display in which monochrome pixels and color pixels are displayed in combination.

[ means for solving the problems ]

According to the present invention, there is provided an image processing apparatus including a saturation value acquisition unit that acquires a saturation value of a target pixel or a saturation value of a target small area including the target pixel and peripheral pixels around the target pixel, and a correction unit that corrects the target pixel so that a corrected gradation characteristic obtained by correcting the target pixel coincides with a gradation characteristic obtained by mixing a color gradation characteristic and a monochrome gradation characteristic at a predetermined mixing ratio based on the saturation value, wherein if the saturation value is c and the mixing ratio of the color gradation characteristic is W, the value of W when c is a variable is represented by w=f (c), and the following condition is satisfied,

conditions are as follows: when the relationship in which the mixing ratio W is proportionally increased with respect to the saturation value c is w=g (c), if the saturation value is equal to or greater than a threshold value, there are a saturation value c satisfying f (c) > αg (c) and a multiplier α, and α is equal to or greater than 1.

Thus, the relationship between the saturation of the target pixel and the mixing ratio of the color gradation characteristics can be changed when the saturation of the target pixel exceeds a predetermined threshold, the mixing ratio of the color gradation characteristics can be suppressed when the saturation of the target pixel is low, and the mixing ratio of the color gradation characteristics can be improved when the saturation of the target pixel is high. Therefore, correction to increase the luminance value of the target pixel is achieved when the saturation of the target pixel is high, and display can be performed with a more appropriate luminance value. Further, since the saturation value of the region unit is not used, the collapse of the screen display due to the difference in saturation value between the regions does not occur.

Various embodiments of the present invention are illustrated below. The embodiments shown below may be combined with each other. Each feature is independently established by the invention.

Preferably, the correction unit includes a mixing unit that determines a mixing ratio of a color gradation characteristic for a color pixel and a monochrome gradation characteristic for a monochrome pixel based on the obtained saturation value.

Preferably, the relation f (c) includes a relation w1=f1 (c) equal to or smaller than the threshold value and a relation w2=f2 (c) equal to or larger than the threshold value, and f1 (c 1). Ltoreq.f2 (c 2) is satisfied if any saturation value equal to or smaller than the threshold value is c1 and any saturation value equal to or larger than the threshold value is c 2.

Preferably, the relation f1 (c) equal to or smaller than the threshold value is a proportional function.

Preferably, there is a 2 nd threshold when the threshold is made to be a 1 st threshold, the 2 nd threshold being equal to or greater than the 1 st threshold, and the inclination of the relation f2 (c) tends to be zero when the saturation value is equal to or greater than the 2 nd threshold.

Preferably, the relation f (c) is at least part of an S-type function.

Preferably, the correction unit further determines the blending ratio W and corrects the color gradation characteristic of the target pixel by using a relationship set so that the larger the difference between the luminance value of the color gradation characteristic of the target pixel and the luminance value of the monochrome gradation characteristic of the target pixel is, the larger the threshold value is.

According to another aspect of the present invention, there is provided an image processing method including: an acquisition step of acquiring a saturation value of a target pixel or a saturation value of a target small region including the target pixel and peripheral pixels around the target pixel; the correction step corrects the target pixel so that the corrected gradation characteristic obtained by correcting the target pixel matches a gradation characteristic obtained by mixing a color gradation characteristic and a monochrome gradation characteristic at a predetermined mixing ratio based on the saturation value, and if the saturation value is c and the mixing ratio of the color gradation characteristic is W, the value of W when c is a variable is expressed by the relation w=f (c) and the following condition is satisfied,

conditions are as follows: if the relationship in which the mixing ratio increases proportionally from the minimum value to the maximum value is w=g (c) as the saturation value increases from the minimum value to the maximum value, then when the saturation value is equal to or greater than a threshold value, there are a saturation value c and a multiplier α that satisfy f (c) > αg (c), and α is equal to or greater than 1.

According to another aspect of the present invention, there is provided an image processing program for causing a computer to function as an image processing apparatus including a saturation value acquisition unit and a correction unit, wherein the image processing program causes the computer to execute an acquisition step of acquiring a saturation value of a target pixel or a saturation value of a target small region including the target pixel and peripheral pixels around the target pixel by the saturation value acquisition unit; and correcting the target pixel by the correction unit so that the corrected gradation characteristic obtained by correcting the target pixel matches a gradation characteristic obtained by mixing a color gradation characteristic and a monochrome gradation characteristic at a predetermined mixing ratio based on the saturation value, wherein if the saturation value is c and the mixing ratio of the color gradation characteristic is W, the value of W when c is a variable is expressed by the relation w=f (c), and the following condition is satisfied: if the relationship in which the mixing ratio increases proportionally from the minimum value to the maximum value is w=g (c) as the saturation value increases from the minimum value to the maximum value, then when the saturation value is equal to or greater than a threshold value, there are a saturation value c and a multiplier α that satisfy f (c) > αg (c), and α is equal to or greater than 1.

[ description of the drawings ]

Fig. 1 is a graph showing GSDF curves and γ2.2 curves.

Fig. 2 is a hardware configuration diagram of the image processing apparatus 100 according to embodiment 1.

Fig. 3 is a functional block diagram of the control unit 1.

In fig. 4, fig. 4A is a diagram showing a lookup table L1 for a monochrome pixel. Fig. 4B is a diagram showing a lookup table L2 for color pixels.

Fig. 5 is a diagram showing a relationship between the saturation value c and the mixing ratio W.

Fig. 6 illustrates a process flow of the sequence of the correction process.

Fig. 7A is a graph showing a relationship between the saturation value and the mixing ratio in modification 1. Fig. 7B is a graph showing a relationship between the saturation value and the mixing ratio in modification 2. Fig. 7C is a graph showing a relationship between the saturation value and the mixing ratio in modification 3.

Fig. 8A is a graph showing the difference between the luminance values of the GSDF curve and the γ2.2 curve. Fig. 8B is a graph showing a difference ratio of luminance values of the GSDF curve and the γ2.2 curve.

In fig. 9, fig. 9A is a diagram of dividing the input gray value into regions for each difference ratio in fig. 8B. Fig. 9B is a diagram defining a relationship between a plurality of saturation values c and a mixing ratio W so as to correspond to the division of the input gray scale value.

Fig. 10 illustrates a process flow of the procedure of the correction process of embodiment 2.

[ detailed description ] of the invention

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In particular, in the present specification, "part" means, for example, a combination of hardware resources implemented by a generalized circuit and information processing of software that can be realized by these hardware resources.

The broad sense of a circuit is a circuit implemented by combining at least a circuit (circuit), a circuit class (circuit), a Processor (Processor), a Memory (Memory), and the like. I.e., including application specific integrated circuits (Applicatoin Specific Integrated Circuit: ASICs), programmable logic devices (e.g., simple programmable logic devices (Simple Programmable Logic Device: SPLDs), complex programmable logic devices (Complex programmable Logic device: CLPDs), and field programmable gate arrays (Field Programmable Gate Array: FPGAs)), etc.

In this specification, a single pixel of an input image or a region including the pixel and peripheral pixels around the pixel is defined as a small region. The image is composed of a static image and a dynamic image, and in the case of the dynamic image, 1 frame is defined unless otherwise specified.

In the following embodiments, various kinds of information and concepts including the information are described, but these represent the level of a signal value as a bit set of 2-ary numbers composed of 0 or 1, and communication and computation can be performed on a broad range of circuits. Specifically, "small region", "input gray value", "saturation value", "luminance value", and the like may be included in such information/concept. These will be described in detail again as necessary.

Embodiment 1

(1.1. Constitution of image processing apparatus 100)

The configuration of the image processing apparatus 100 is described with reference to fig. 2. In the description using fig. 2, only the basic functions of each component will be described, and the processing will be specifically described later.

As shown in fig. 2, the image processing apparatus 100 includes a control unit 1, a storage unit 2, an operation unit 3, a display unit 4, a backlight 5, a communication unit 6, and a bus 7. The control unit 1 reads a program (not shown) stored in the storage unit 2 and executes various arithmetic processing, for example, a CPU or the like.

The storage unit 2 stores a lookup table for gradation characteristic correction applied to the display unit 4, or various data or programs, for example, a memory, HDD, or SSD. Here, the program may be installed in advance at the time of shipment of the image processing apparatus 100, downloaded as an application program on a website, or transferred from another information processing apparatus or a recording medium via wired or wireless communication. The look-up table is described in detail later.

The operation unit 3 operates the image processing apparatus 100, and is configured by an operation recognition apparatus using, for example, a switch, a button, a mouse, a keyboard, a touch panel, a voice input unit, or a camera. For example, various setting information on OSD (On Screen Display) is operated by the operation unit 3.

The display unit 4 displays input image data (static image and dynamic image) as an image, and is configured by a liquid crystal display, an organic EL display, a touch panel display, electronic paper, or other displays, for example.

The backlight 5 illuminates the display section 4 from the back of the display section 4. When the display unit 4 is not a liquid crystal display, the backlight 5 is not required.

The communication unit 6 transmits or receives various data of another information processing apparatus or each component, and is composed of an arbitrary I/O. The bus 7 is composed of a serial bus, a parallel bus, or the like, and is electrically connected to each section to be able to transmit or receive various data.

Each component may be realized by software or hardware. When implemented in software, the various functions may be implemented by the CPU executing a program. The program may be stored in the built-in storage unit 2 or may be stored in a computer-readable non-transitory recording medium. The program stored in the external storage unit is read out and may be realized by so-called cloud computing. When implemented in hardware, the circuit can be implemented by various circuits such as an ASIC, an FPGA, or a DRP.

(1.2. Functional constitution)

The function of the control unit 1 will be described with reference to fig. 3. As shown in fig. 3, the control unit 1 includes a determination unit 11, a saturation value acquisition unit 12, and a correction unit 20. The correction unit 20 includes a mixing unit 21, a monochrome correction unit 22, and a color correction unit 23.

The determination unit 11 determines whether or not the target pixel of the input image data input to the image processing apparatus 100 is monochrome or color. Here, various methods are known as the determination method. As an example, the following method may be employed: an input gray value (R, G, B) having a target pixel is plotted in an RGB space, and a distance from a straight line defined in a (1, 1) direction in the RGB space falls within a reference value, and it is determined that the image is monochrome. In the present embodiment, the input gradation value is defined as a 10-bit digital value having a value of 0 to 1023.

The saturation value obtaining unit 12 obtains a saturation value (hereinafter also referred to as a saturation value c) based on the input gradation value for a target pixel of the input image data input to the image processing apparatus 100. In the present embodiment, the saturation value is defined as an 8-bit digital value that takes a value of 0 to 255. Here, the saturation value obtaining unit 12 may obtain a saturation value of a target small area including the target pixel and surrounding pixels. In this case, for example, the saturation values corresponding to the target pixel and the surrounding pixels may be calculated as the saturation value of the target small region by adding the saturation values together, or 1 saturation value in the target small region may be obtained as the representative value.

The correction unit 20 performs color gradation characteristic correction for color pixels and monochrome gradation characteristic correction for monochrome pixels on the input image data. Here, the gradation characteristic refers to a relationship between an input gradation value of a target pixel of input image data and a luminance value of the target pixel at the time of display output. The color gradation characteristic correction means correcting the gradation characteristic of the color pixels. The monochrome gradation characteristic correction means that gradation characteristics of monochrome pixels are corrected.

The mixing unit 21 determines a mixing ratio (hereinafter referred to as a mixing ratio W) of the color gradation characteristic and the monochrome gradation characteristic based on the saturation value acquired by the saturation value acquiring unit 12. The details of the specific processing of the mixing section 21 will be described later.

The monochrome correction section 22 performs monochrome gradation characteristic correction for each target pixel of the input image data. The details of the specific processing of the monochrome gradation characteristic correction by the monochrome correction section 22 will be described later.

The color correction section 23 performs color gradation characteristic correction for each target pixel of the input image data. The details of the specific processing of the color gradation characteristic correction by the color correction section 23 will be described later.

As an example, the storage unit 2 stores a lookup table L for performing gradation characteristic correction and a mixing ratio table K defining a relationship between the saturation value c and the mixing ratio W.

The display unit 4 is configured to display the input image data at a luminance value corresponding to the gradation characteristic corrected by the monochrome correction unit 22 or the color correction unit 23 for the target pixel of the input image data.

(1.3. Look-up table)

Referring to fig. 4A and 4B, the lookup table L stored in the storage unit 2 will be described. The method for defining the lookup table L is only an example, but is not limited to the method illustrated here.

As shown in fig. 4A and 4B, the storage unit 2 stores a lookup table L1 for monochrome pixels and a lookup table L2 for color pixels. The lookup table L1 defines input gray-scale values of 0 to 1023 and luminance values corresponding thereto. Here, the luminance values M0 to M1023 are values that can be represented by 0 to 100%, 0% representing the lowest luminance that can be represented by the display section 4, and 100% representing the maximum luminance that can be represented by the display section 4. In the lookup table L1, the input gradation value corresponds to the luminance value 1 to 1 so as to satisfy the GSDF curve specified by the DICOM standard. The luminance value may be defined as a 16-bit digital value, for example, a value of 0 to 65535, instead of 0 to 100%.

On the other hand, the lookup table L2 defines an input gradation value and a luminance value of each RGB corresponding thereto. In the lookup table L2, a relationship specified by the lookup table L1 is specified for each RGB. That is, the luminance values R0 to R1023 correspond to R (red), the luminance values G0 to G1023 correspond to G (green), and the luminance values B0 to B1023 correspond to B (blue), respectively. In the lookup table L2, the input gradation value and the luminance value correspond to 1 for each RGB1 in such a manner as to satisfy the γ2.2 curve specified by the sRGB standard.

Thus, the gradation characteristic correction can be performed so that the input gradation value of the monochrome pixel becomes a luminance value satisfying the GSDF curve by referring to the lookup table L1. Further, the gradation characteristic correction can be performed by referring to the lookup table L2 so that the input gradation value of the color pixel becomes a luminance value satisfying the γ2.2 curve.

(1.4. Mixing section 21)

The mixing unit 21 determines a mixing ratio W for mixing the color gradation characteristic for the color pixels (corresponding to the lookup table L2) and the monochrome gradation characteristic for the monochrome pixels (corresponding to the lookup table L1) based on the saturation value c acquired by the saturation value acquiring unit 12. Here, the mixing ratio W means a color gradation characteristic when w=1, and a monochrome gradation characteristic when w=0. When w=0.5, the gray-scale characteristics are synthesized by mixing the color gray-scale characteristics and the monochrome gray-scale characteristics by 50% respectively.

The relationship between the saturation value c and the mixing ratio W is defined in the mixing ratio table K stored in the storage unit 2. The mixing unit 21 may determine the mixing ratio W corresponding to the saturation value c acquired by the saturation value acquiring unit 12 by referring to the mixing ratio table K.

Fig. 5 is a diagram showing a relationship w=f (c) (hereinafter also referred to as a correspondence relationship f (c)) between a saturation value c and a mixing ratio W, and corresponds to a mixing ratio table K. Fig. 5 also shows a relationship w=g (c) (hereinafter also referred to as a proportional relationship g (c)) in which the mixing ratio W increases proportionally from the minimum value 0 to the maximum value 1 as the saturation value c increases from the minimum value 0 to the maximum value 255. Further, the 1 st threshold P and the 2 nd threshold Q with respect to the saturation value c are shown.

As shown in fig. 5, the correspondence relation f (c) is configured such that a value larger than the proportional relation g (c) can be taken in a region where the saturation value c is equal to or larger than the 1 st threshold P (i.e., a region after the point X of f (c)). In other words, when the saturation value c is equal to or greater than the 1 st threshold P, there are a saturation value c satisfying the condition of f (c) > αg (c) and a multiplier α, α Σ be equal to or greater than 1.

With such a configuration, the mixing ratio W of the color gradation characteristics can be increased when the 1 st threshold P is equal to or greater than the proportional relationship g (c) in which the mixing ratio W of the color gradation characteristics is increased in proportion to the increase of the saturation value c. As a result, when equal to or greater than the 1 st threshold P, the ratio of the color gradation characteristic to the input pixel increases, and an image with a further improved luminance value can be realized.

The value of the number of passengers α is 1 to 20, preferably 1.5 to 15, and more preferably 2 to 10. The value of α is specifically, for example, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, 10, 10.5, 11, 11.5, 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, 18, 18.5, 19, 19.5, 20, but may also fall within the range between any 2 values exemplified herein.

Here, when the saturation value c is equal to or greater than the 1 st threshold P, the saturation value of the ratio equal to or greater than 50% among the saturation values from the 1 st threshold P to the maximum value 255 satisfies the above condition. The ratio is specifically 50%,55%,60%,65%,70%,75%,80%,85%,90%,95%, and may be in the range between any 2 values exemplified herein. More preferably, the ratio may be 70%. At this time, the mixing ratio at which the mixing ratio of the color gradation characteristics can be made larger than the proportional relation g (c) for 70% or more of the saturation value c of the 1 st threshold P or more, and an image with an increased luminance value can be presented for 70% or more of the saturation value c of the 1 st threshold P or more.

Further, it is preferable that, when the saturation value c is equal to or greater than the 1 st threshold P, among the saturation values from the 1 st threshold P to the maximum value 255, the saturation value included in the region of 50% or greater whose value is lower satisfies the above condition. This region is specifically 50%,55%,60%,65%,70%,75%,80%,85%,90%,95% lower in value, and may be in the range between any 2 values exemplified herein. More preferably, the ratio may be set to 90%. In this way, in the correspondence relation (c), the mixing ratio of the color gradation characteristics can be increased in the region of 90% of the saturation value from the 1 st threshold P to the maximum value 255. As a result, in the saturation value from the 1 st threshold P to the maximum value 255, an image with an increased luminance value can be presented in a region with a value equal to or greater than 90% that is lower.

In the example shown in fig. 5, the relationship f (c) between the saturation value c and the mixing ratio W includes a relationship w=f1 (c) equal to or smaller than the 1 st threshold P and a relationship w=f2 (c) equal to or larger than the 1 st threshold P, and f1 (c 1) +.f2 (c 2) is satisfied when any saturation value equal to or smaller than the 1 st threshold P is c1 and any saturation value equal to or larger than the 1 st threshold P is c 2.

In the example of fig. 5, f1 (c) is a proportional function, and matches the proportional relationship g (c). On the other hand, in the example of fig. 5, f2 (c) uses at least a part of the S-type function. Here, f1 (c) and f2 (c) are not limited to this, and the relationship of f1 (c 1). Ltoreq.f2 (c 2) may be satisfied. In this way, by setting f1 (c) as a proportional function, the mixing ratio of the monochrome gradation characteristic can be improved in the region where the saturation value c is low. In this way, in the region where the saturation value c is low, noise generated due to the high mixing ratio of the color gradation characteristics can be suppressed, and the ratio increase of the monochrome gradation characteristics can be prevented from being excessively large and greatly deviated from the predetermined color display.

In addition, f (c) increases in inclination in a region where the saturation value c is equal to or greater than the 1 st threshold P and equal to or less than the 2 nd threshold, so that the value of the mixing ratio W increases greatly. In addition, in a region where the saturation value c is equal to or greater than the 2 nd threshold value and equal to or less than the maximum value 255 (i.e., a region after the point Y in f (c)), the inclination thereof tends to be zero, and f (c) gradually increases.

By defining the relationship between the saturation value c and the mixing ratio W in this way, the mixing ratio of the color gradation characteristics can be increased in the region equal to or greater than the 1 st threshold P while the gradation characteristic correction for mixing the monochrome gradation characteristics and the color gradation characteristics is performed while suppressing the mixing ratio of the color gradation characteristics in the region where the saturation value c is low.

(1.5. Monochromatic correction unit 22)

The monochrome correction portion 22 refers to the lookup table L1 to obtain a luminance value for the input gradation value of the target pixel determined as the monochrome pixel by the determination portion 11. As described above, the lookup table L1 is specified to satisfy the GSDF curve. As a result, the monochrome pixels can be displayed with the luminance values satisfying the GSDF curve.

Then, the monochrome correction section 22 refers to the lookup table L1 to determine the luminance value for blending based on the blending ratio W for the input gradation value of the target pixel determined as the color pixel by the determination section 11.

(1.6. Color correction portion 23)

For the input gradation value of the target pixel determined as a color pixel by the determination section 11, the color correction section 23 refers to the lookup table L1 and determines a luminance value for blending based on the blending ratio W.

The control unit 1 displays the pixels determined by the determination unit 11 as monochrome pixels on the display unit 4 based on the luminance value determined by the monochrome correction unit 22. On the other hand, the control unit displays the pixels determined as color pixels by the determination unit 11 on the display unit 4 based on the luminance value determined by the monochrome correction unit 22 and the luminance value determined by the color correction unit 23.

The luminance value at the time of displaying a color pixel will be specifically described below. As an example, when the input gradation value of the target pixel is (R, G, B) = (80, 90, 100) and the mixing ratio W of the color gradation characteristics is 0.7, the luminance values (MR, MG, MB) after mixing are obtained from the following (equations 1) to (3).

Mr=l2 (80) ×0.7+l1 (80) ×0.3 (formula 1)

Mg=l2 (90) ×0.7+l1 (90) ×0.3 (formula 2)

Mb=l2 (100) ×0.7+l1 (100) ×0.3 (formula 3)

Here, the luminance value of the lookup table L1 when the input value is 80 is L1 (80), and the luminance value of the lookup table L2 is L2 (80). The same is true for the other input values 90, 100.

(1.7. Sequence of correction processing)

The procedure of the correction process in the present embodiment will be described with reference to fig. 6. The following processing is executed by the control unit 1 configured by a CPU, for example.

In step S10, the determination unit 11 performs a monochrome determination on the target pixel of the input image data. When the determination section 11 determines that the input pixel is monochrome, step S45 is performed. On the other hand, when the determination unit 11 determines that the input pixel is color, step S20 is performed.

In step S20, the saturation value obtaining unit 12 obtains a saturation value c for the target pixel or the target small region determined to be color by the determining unit 11.

Next, in step S30, the mixing unit 21 refers to the mixing ratio table K stored in the storage unit 2 based on the acquired saturation value c, and determines the mixing ratio W of the color gradation characteristics.

Next, in step S40, the monochrome correction section 22 and the color correction section 23 refer to the lookup tables L1 and L2 based on the input gradation value of the input pixel, and the luminance value is a gradation-corrected luminance value synthesized by mixing the values of the lookup tables L1 and L2 based on the mixing ratio W determined in step S30.

On the other hand, in step S45, for the target pixel determined to be monochrome by the determination unit 11, the monochrome correction unit 22 refers to the lookup table L1 stored in the storage unit 2, and determines a luminance value corresponding to the input gradation value of the target pixel.

In step S50, the correction unit 20 determines whether or not the processing in S10 to S45 is completed for all pixels of the input image data. When the process is not ended, step S10 is executed again. On the other hand, when the process ends, step S60 is performed.

In step S60, the control unit 1 controls the display unit 4 so that the input image data is displayed at the luminance value determined in step S40 and/or step S45.

As described above, in the present embodiment, the control unit 1 includes the saturation value acquisition unit 12 and the correction unit 20. The saturation value obtaining unit 12 obtains a saturation value of a target pixel or a target small region of the input image data. The correction section 20 corrects the target pixel based on the acquired saturation value in the following manner: the corrected gradation characteristic obtained by correcting the target pixel matches the gradation characteristic synthesized by mixing the color gradation characteristic for the color pixel and the monochrome gradation characteristic for the monochrome pixel at a predetermined mixing ratio.

Here, when the saturation value is c and the mixing ratio of the color gradation characteristics is W, the correspondence relationship w=f (c) of the mixing ratio W when c is a variable, there is a condition that the ratio relationship g (c) satisfies f (c) > αg (c) and the saturation value c and the number α satisfy α.gtoreq.1.

With the above configuration, the mixing ratio W of the color gradation characteristics can be improved in the region equal to or larger than the 1 st threshold P, as compared with the case defined by the proportional relation g (c). As a result, in the region equal to or larger than the 1 st threshold P, the gradation characteristic based on the mixture can be made close to the gradation characteristic based on the γ2.2 curve.

(1.8. Modification)

Fig. 7A shows a correspondence f (c) between the saturation value c and the mixing ratio W as modification 1. In this example, the correspondence w=f (c) of the mixing ratio W with respect to the saturation value c is expressed as 1S-shaped function. Specifically, the correspondence f (c) is expressed by the following formula.

[ number 1 ]

Here, regarding the coefficients a and b, a=18, b=128 in the example shown in fig. 7A, but is not limited to this example. Thus, the relationship between the saturation value and the mixing ratio can be defined by using 1 function to satisfy the above condition, and the definition of the correspondence relation f (c) can be facilitated.

Fig. 7B shows a correspondence f (c) between the saturation value c and the mixing ratio W as modification 2. In this example, in the correspondence relationship w=f (c) of the mixing ratio W to the saturation value c, f1 (c) is a linear function, and f2 (c) is a constant number. Thus, the mixing ratio W with respect to the saturation value c can be obtained by a simpler operation.

Fig. 7C shows a correspondence f (C) between the saturation value C and the mixing ratio W as modification 3. In this example, the correspondence f (c) < the proportional relationship g (c) until the saturation value c reaches the threshold P. In this case, the same effects as those of the above embodiment can be obtained.

Here, in fig. 7C, the relationship of the saturation value C and the mixing ratio W is not limited to monotonically increasing until the threshold P is reached. The mixing ratio W may be 0, for example, when it is equal to or smaller than the threshold value P. Specifically, as shown by stippling in fig. 7C, an arbitrary threshold between 0 and P may be S, w=0 up to 0C S, and when C S, W monotonically increases toward f (P).

The reason why the mixing ratio of the monochrome gradation characteristic is improved when the saturation value c is low in the above embodiment will be described below. In a low-saturation image in which a monochrome pixel and a color pixel are mixed, if the difference between luminance values of the monochrome gray scale characteristic for the monochrome pixel and the color gray scale characteristic for the color pixel is large, the difference may be perceived as noise by a user. Accordingly, gradation characteristic correction to improve the mixing ratio of the monochrome gradation characteristic is required for the color pixels of the low-saturation image so as not to be perceived as noise.

Similarly, in a high saturation image in which a monochrome pixel and a color pixel are mixed, when the difference between luminance values of the monochrome gray scale characteristic and the color gray scale characteristic is large, the difference may be perceived as noise. However, in a high saturation image, noise is rarely perceived. The reason for this is that since the luminance of color (RGB colors) is lower than that of monochrome, it is difficult for the user to feel the difference in luminance at high saturation.

Further, for another reason, it is possible to easily perceive a difference due to color difference in a low-saturation image, but it is difficult to perceive a difference due to color difference in a high-saturation image. In this way, in a high saturation image, even if the mixing ratio of the color gradation characteristics is increased, the occurrence of noise is to an extent that is hardly perceived by the user. In addition, in the case of high saturation, by increasing the mixing ratio of the color gradation characteristics, it is possible to prevent a color image displayed on the display from being perceived as dark without degrading the image quality.

< 2. Embodiment 2 >

In embodiment 2, the correspondence F (c) between the saturation value c and the mixing ratio W is defined by considering the difference between the luminance value defined by the GSDF curve for the input gradation value and the luminance value defined by the γ2.2 curve, and is different from embodiment 1. Note that the same reference numerals are given to the same components as those in embodiment 1, and the description thereof will not be repeated.

Fig. 8A shows GSDF curves and γ2.2 curves. Here, the luminance value on the γ2.2 curve when the input gradation value is Z is B1, and the luminance value on the GSDF curve is B2. As shown in fig. 8A, the difference between the luminance value B1 and the luminance value B2 varies according to the input gradation value.

Fig. 8B shows a difference ratio C between the luminance value B1 and the luminance value B2 based on fig. 8A. Here, the differential ratio C is calculated by the following (expression 4).

C= | (B1-B2)/b2| (|is an absolute value) (formula 4)

Here, a large difference between the luminance value B1 and the luminance value B2 for the input gradation value means that the difference between the corrected luminance value corrected by the monochrome gradation characteristic of the GSDF curve and the corrected luminance value corrected by the color gradation characteristic of the γ2.2 curve is large. At this time, if the mixing ratio W of the color gradation characteristics is rapidly increased, noise is generated, and the image quality is degraded.

Then, as shown in fig. 9A, the regions I to IV are defined according to the magnitude of the difference ratio between the luminance value B1 and the luminance value B2. The input gradation values corresponding to the regions I to IV are defined as the regions (1) to (4).

As shown in fig. 9B, a plurality of correspondence relationships between the saturation values c such as F1 (c) to F (c) and the mixing ratio W are prepared. Here, in fig. 8B and 9, the correspondence relation F1 (c) is applied to the input gradation value belonging to the region (corresponding to the region (1)) where the difference between the luminance value B1 and the luminance value B2 is minimum. The correspondence F2 (c) is applied to the input gradation value in the region (corresponding to the region (2)) where the difference between the luminance value B1 and the luminance value B2 is the second smallest. Accordingly, the correspondence relations F1 (c) to F4 (c) for determining the mixing ratio are determined based on the input gradation value.

Here, as the input gradation values at the time of determining the correspondence relations F1 (c) to F4 (c), 3 addition averages of the input gradation values (R, G, B) having the target pixels may be used, or a specific 1 out of 3 may be used as a representative value.

The relationships F1 (c) to F4 (c) can be specifically realized by changing the coefficient b in the above-mentioned [ number 1 ]. As an example, the S-type function described in the above [ number 1 ] of a=18, b=55, a=18, b=70, a=18, b=96, a=18, b=128 in F1 (c), F2 (c), and F3 (c) is included.

In addition, of the 1 st threshold values P1 to P4 corresponding to the relationships F1 (c) to F4 (c), P1 is smallest, P2 and P3 are larger, and P4 is largest (p1.ltoreq.p2.ltoreq.p3.ltoreq.p4). In other words, the larger the difference ratio C between the luminance value B1 and the luminance value B2 is, the larger the 1 st threshold value is. Mixing ratio tables K1 to K4, in which the correspondence relationships F1 (c) to F4 (c) set in this manner are defined, are stored in the storage unit 2.

The mixing section 21 refers to the mixing ratio table K corresponding to the input gradation value of the target pixel to determine the mixing ratio W. In addition, as in the above embodiment, the color correction unit 23 refers to the lookup tables L1 and L2 based on the determined mixing ratio W, and performs gradation characteristic correction on the input gradation value.

With such a configuration, when the input gradation value is large in the absolute value of the difference between the luminance value defined by the GSDF curve and the luminance value defined by the γ2.2 curve, the mixing ratio of the color gradation characteristics can be suppressed when the saturation is low. In addition, even when the difference is small, the mixing ratio can be increased when the chroma is low. As a result, an appropriate mixing ratio can be determined from the input gradation value.

Referring to fig. 10, the procedure of the correction process in embodiment 2 will be described. Note that the same processing as in embodiment 2 is denoted by the same reference numerals, and description thereof will not be repeated.

In step S25 subsequent to step S20, the correction unit 20 determines the relation F (c) to be applied to the target pixel based on the input gradation value of the target pixel. Next, step S30 is performed to determine the blending ratio W for the target pixel.

< 3 other embodiments >

The application of the present invention is not limited to the above embodiment. For example, the 3D-1D lookup table may be applied to a common 1D lookup table for color and monochrome after referring to a 3D lookup table for defining the gradation characteristic of color.

A method of determining a 3D lookup table in which luminance values as a mixing result are defined on the basis of a mixing ratio W that satisfies the luminance value of the GSDF curve, the luminance value that satisfies the γ2.2 curve, and the saturation value c may be used.

Further, a method of defining a 3D lookup table on the axis R, G, B of the input gradation values, in which a luminance value to be a gradation characteristic, which is synthesized by mixing a color gradation characteristic and a monochrome gradation characteristic at a mixing ratio W based on a saturation value c, is also available.

Instead of the lookup table, an arithmetic expression may be used to output a luminance value that is a gradation characteristic obtained by mixing the color gradation characteristic and the monochrome gradation characteristic at the mixing ratio W based on the saturation value c.

In the above embodiment, the value (luminance value) of the lookup table L1 for monochrome and the lookup table L2 for color are mixed for each pixel based on the mixing ratio W, but the luminance value may be determined by performing an operation of a correction coefficient based on the mixing ratio W on the input gradation value of the input pixel (or by performing the same processing using the lookup table), thereby utilizing the gradation characteristic obtained by mixing the color gradation characteristic and the monochrome gradation characteristic at the mixing ratio W based on the saturation value c.

In the above embodiment, the gradation characteristic correction of the color pixels is described as an example of the gradation characteristic correction satisfying the luminance value of the γ2.2 curve, but the gradation characteristic correction is not limited to the γ2.2 curve, and for example, the Gamma value may be a value of 1.8 to 2.6, and gradation characteristics satisfying the luminance value of rec.709, PQ scheme (Perceptual Quantization), HLG scheme (Hybrid Log Gamma), or the like may be employed.

Further, an image processing program is realized in which a computer is caused to function as an image processing apparatus including a saturation value acquisition unit and a correction unit, the image processing program being characterized in that the computer is caused to execute an acquisition step of acquiring a saturation value of a target pixel or a saturation value of a target small region including the target pixel and peripheral pixels around the target pixel by the saturation value acquisition unit; and correcting the target pixel by the correction unit so that the corrected gradation characteristic obtained by correcting the target pixel matches a gradation characteristic obtained by mixing a color gradation characteristic and a monochrome gradation characteristic at a predetermined mixing ratio based on the saturation value, wherein if the saturation value is c and the mixing ratio of the color gradation characteristic is W, the value of W when c is a variable is expressed by the relation w=f (c), and the condition is satisfied.

In addition, the present invention can be realized as a computer-readable non-transitory recording medium storing the above-described program.

Various embodiments of the present invention have been described, but these are presented by way of example only and are not meant to limit the scope of the invention. These novel embodiments may be implemented in other various ways, and various omissions, substitutions, and changes may be made without departing from the gist of the invention. The present embodiment or the modifications thereof are included in the scope and gist of the invention and are included in the invention described in the scope of the claims and the scope equivalent thereto.

[ description of the symbols ]

1: indication control part

2: storage part

3: operation part

4: display unit

5: backlight lamp

6: communication unit

7: bus line

11: determination unit

12: saturation value acquisition unit

13: mixing part

20: correction part

21: mixing part

22: monochrome correction part

23: color correction unit

100: image processing apparatus and method

K: mixing ratio meter

L: lookup table

Claims

1. An image processing apparatus including a saturation value acquisition unit and a correction unit, the image processing apparatus comprising,

the saturation value obtaining unit obtains a saturation value c of a target pixel or a saturation value c of a target small region including the target pixel and peripheral pixels around the target pixel,

the correction unit corrects the target pixel so that the corrected gradation characteristic obtained by correcting the target pixel matches the gradation characteristic obtained by mixing the color gradation characteristic and the monochrome gradation characteristic at a predetermined mixing ratio W based on the saturation value c,

when the saturation value c is lower than a threshold value, the predetermined mixing ratio W is a value according to a proportional relation w=g (c) in which the mixing ratio W increases in proportion to the saturation value c, or a value smaller than a value according to the proportional relation w=g (c),

when the saturation value c is equal to or greater than the threshold value, the predetermined mixing ratio W is a value according to the relationship w=f (c), and f (c) > αg (c), α is equal to or greater than 1 for each saturation value c.

2. The image processing apparatus according to claim 1, wherein,

the correction unit includes a mixing unit that determines a mixing ratio of a color gradation characteristic for a color pixel and a monochrome gradation characteristic for a monochrome pixel based on the obtained saturation value c.

3. The image processing apparatus according to claim 1, wherein,

the relation f (c) includes

A relation w1=f1 (c) equal to or smaller than the threshold value

A relation w2=f2 (c) equal to or greater than the threshold value,

if any saturation value equal to or smaller than the threshold value is set as c1, any saturation value equal to or larger than the threshold value is set as c2,

and f1 (c 1) is less than or equal to f2 (c 2).

4. The image processing apparatus according to claim 3, wherein,

the relation f1 (c) equal to or smaller than the threshold value is a proportional function.

5. The image processing apparatus according to claim 3, wherein,

there is a 2 nd threshold when the threshold is made to be a 1 st threshold,

the 2 nd threshold is equal to or greater than the 1 st threshold,

when the saturation value c is equal to or greater than the 2 nd threshold, the inclination of the relation f2 (c) tends to be zero.

6. The image processing apparatus according to claim 1, wherein,

the relation f (c) is at least part of an S-type function.

7. The image processing apparatus according to any one of claims 1 to 6, wherein,

the correction unit further determines the mixing ratio W and corrects the color gradation characteristic of the target pixel by using a relationship set so that the larger the difference between the luminance value of the color gradation characteristic of the target pixel and the luminance value of the monochrome gradation characteristic of the target pixel is, the larger the threshold value is.

8. An image processing method, comprising:

an acquisition step of acquiring a saturation value c of a target pixel or a saturation value c of a target small region including the target pixel and peripheral pixels around the target pixel; and

a correction step of correcting the target pixel so that a corrected gradation characteristic obtained by correcting the target pixel coincides with a gradation characteristic synthesized by mixing a color gradation characteristic and a monochrome gradation characteristic at a predetermined mixing ratio W based on the saturation value c,

9. A recording medium which is a non-transitory recording medium readable by a computer and storing an image processing program for causing the computer to function as an image processing apparatus including a saturation value acquisition unit and a correction unit, the recording medium being characterized in that the image processing program causes the computer to execute

A saturation value obtaining step of obtaining a saturation value c of a target pixel or a saturation value c of a target small region including the target pixel and peripheral pixels around the target pixel by the saturation value obtaining unit; and

a step of correcting the target pixel by the correction unit so that the corrected gradation characteristic obtained by correcting the target pixel matches a gradation characteristic obtained by mixing a color gradation characteristic and a monochrome gradation characteristic at a predetermined mixing ratio W based on the saturation value c,